ioemu: pump SDL events on resize

ioemu: pump SDL events on resize

When sdl_resize resizes the SDL window, some window manager send back
a ConfigureNotify event, which triggers a SDL_VIDEORESIZE event. That
event, however, is seen only much later, on the next VGA refresh
round. If the guest quickly switches to another resolution in between,
the SDL_VIDEORESIZE event makes us erroneously rescale that new
resolution into the old one.

This patch makes us pump that window manager event, so that no
SDL_VIDEORESIZE event is generated.

Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>